The ~ operator is overloaded for two types of operands: number and BigInt. For numbers, the operator returns a 32-bit integer. For BigInts, the operator returns a BigInt. It first coerces the operand to a numeric value and tests the type of it. It performs BigInt NOT if the operand becomes a BigInt; otherwise, it converts the operand to a 32-bit integer and performs number bitwise NOT.

The operator operates on the operands' bit representations in two's complement. The operator is applied to each bit, and the result is constructed bitwise.

The truth table for the NOT operation is:

 9 (base 10) = 00000000000000000000000000001001 (base 2)
               --------------------------------
~9 (base 10) = 11111111111111111111111111110110 (base 2) = -10 (base 10)

Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32-bit integer:

Before: 11100110111110100000000000000110000000000001
After:              10100000000000000110000000000001

For BigInts, there's no truncation. Conceptually, understand positive BigInts as having an infinite number of leading 0 bits, and negative BigInts having an infinite number of leading 1 bits.

Bitwise NOTing any 32-bit integer x yields -(x + 1). For example, ~-5 yields 4.

Bitwise NOTing any number x twice returns x converted to a 32-bit integer. Do not use ~~x to truncate numbers to integers; use Math.trunc() instead. Due to using 32-bit representation for numbers, both ~-1 and ~4294967295 (2³² - 1) result in 0.

• Bitwise operators in the JS guide